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Degradation of Fe-Mg silicates in hot CO2 atmospheres: Applications to VenusExperiments demonstrated that oxidation of ferromagnesian silicates and magnetite occurs when these minerals are heated at 800 C in 1 atmosphere of CO2, under which conditions hematite is thermodynamically stable. The 30 ppm oxygen impurity in CO2 presumably facilitates the oxidation of some of the ferrous iron initially present in the crystal structures of the minerals. Mossbauer spectral measurements reveal, however, that only CO2 degraded olivine and pigeonite is hematite formed as a magnetically ordered phase at ambient temperatures. In orthopyroxene, some of the ferric iron produced by oxidation is present as nanophase hematite which, because it remains superparamagnetic until 4.2 K, must exist as particles less than or equal to 4 nm in diameter. In the calcic pyroxenes much of the oxidized ferrous iron may still remain as structural Fe3(+) in the host silicates. Some ferric iron may also be present as unit cell sized Fe2O3 inclusions in the pyroxenes, or be segregated along cleavage planes, or be coating mineral grains. In these states of aggregation, the Fe2O3 is unidentifiable by x ray diffraction and in low temperature Mossbauer spectra. Applications of this research to the surface of Venus are discussed.
Document ID
19920001588
Acquisition Source
Legacy CDMS
Document Type
Other
Authors
Straub, Darcy W. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Burns, Roger G. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Date Acquired
September 6, 2013
Publication Date
June 1, 1991
Publication Information
Publication: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990
Subject Category
Lunar And Planetary Exploration
Accession Number
92N10806
Funding Number(s)
CONTRACT_GRANT: NAGW-2037
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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